Western Ghats also known as Sahyadri (Benevolent Mountains) is a mountain range that runs parallel to the western coast of the Indian peninsula, located entirely in India. It is a UNESCOWorld Heritage Site and is one of the eight "hottest hot-spots" of biological diversity in the world.[1][2] It is sometimes called the Great Escarpment of India.[3] The range runs north to south along the western edge of the Deccan Plateau, and separates the plateau from a narrow coastal plain, called Konkan, along the Arabian Sea. A total of thirty-nine properties including national parks, wildlife sanctuaries and reserve forests were designated as world heritage sites - twenty in Kerala, ten in Karnataka, five in Tamil Nadu and four in Maharashtra.[4][5]

The area is one of the world's ten "Hottest biodiversity hotspots" and has over 7,402 species of flowering plants, 1,814 species of non-flowering plants, 139 mammal species, 508 bird species, 179 amphibian species, 6,000 insects species and 290 freshwater fish species; it is likely that many undiscovered species live in the Western Ghats. At least 325 globally threatened species occur in the Western Ghats.[8][9][10]

The Western Ghats extend from the Satpura Range in the north, stretching from Gujarat to Tamil Nadu.[citation needed] It traverses south through the states of Maharashtra, Goa, Karnataka and Kerala. Major gaps in the range are the Goa Gap, between the Maharashtra and Karnataka sections, and the Palghat Gap on the Tamil Nadu and Kerala border between the Nilgiri Hills and the Anaimalai Hills. The mountains intercept the rain-bearing westerly monsoon winds, and are consequently an area of high rainfall, particularly on their western side. The dense forests also contribute to the precipitation of the area by acting as a substrate for condensation of moist rising orographic winds from the sea, and releasing much of the moisture back into the air via transpiration, allowing it to later condense and fall again as rain.

Climate in the Western Ghats varies with altitudinal gradation and distance from the equator. The climate is humid and tropical in the lower reaches tempered by the proximity to the sea. Elevations of 1,500 m (4,921 ft) and above in the north and 2,000 m (6,562 ft) and above in the south have a more temperate climate. Average annual temperature is around 15 °C (59 °F). In some parts frost is common, and temperatures touch the freezing point during the winter months. Mean temperature range from 20 °C (68 °F) in the south to 24 °C (75 °F) in the north. It has also been observed that the coldest periods in the South Western Ghats coincide with the wettest.[17]

During the monsoon season between June and September, the unbroken Western Ghats chain acts as a barrier to the moisture laden clouds. The heavy, eastward-moving rain-bearing clouds are forced to rise and in the process deposit most of their rain on the windward side. Rainfall in this region averages 300 centimetres (120 in) to 400 centimetres (160 in) with localised extremes touching 900 centimetres (350 in). The eastern region of the Western Ghats which lie in the rain shadow, receive far less rainfall of about 100 centimetres (39 in) resulting in an average rainfall of 250 centimetres (98 in) across regions. The total amount of rain does not depend on the spread of the area with areas in northern Maharashtra receiving heavy rainfall followed by long dry spells, while regions closer to the equator receive less annual rainfall and have rain spells lasting several months in a year.[17]

The evergreen forests in Wayanad mark the transition zone between the northern and southern ecologic regions of the Western Ghats. The southern ecologic regions are generally wetter and more species-rich. At lower elevations are the South Western Ghats moist deciduous forests, with Cullenia the characteristic tree genus, accompanied by teak, dipterocarps, and other trees. The moist forests transition to the drier South Deccan Plateau dry deciduous forests, which lie in its rain shadow to the east. Above 1,000 meters are the South Western Ghats montane rain forests, also cooler and wetter than the surrounding lowland forests, and dominated by evergreen trees, although some montane grasslands and stunted forests can be found at the highest elevations. The South Western Ghats montane rain forests are the most species-rich ecologic region in peninsular India; eighty percent of the flowering plant species of the entire Western Ghats range are found in this ecologic region.

Historically the Western Ghats were well-covered in dense forests that provided wild foods and natural habitats for native tribal people. Its inaccessibility made it difficult for people from the plains to cultivate the land and build settlements. After the arrival of the British in the area, large swathes of territory were cleared for agricultural plantations and timber. The forest in the Western Ghats has been severely fragmented due to human activities, especially clear felling for tea, coffee, and teak plantations during 1860 to 1950. Species that are rare, endemic and habitat specialists are more adversely affected and tend to be lost faster than other species. Complex and species rich habitats like the tropical rainforest are much more adversely affected than other habitats.[18]

The area is ecologically sensitive to development and was declared an ecological hotspot in 1988 through the efforts of ecologist Norman Myers. The area covers five percent of India's land with 27% of all species of higher plants in India (4,000 of 15,000 species) are found here and 1,800 of these are endemic to the region. The range is home to at least 84 amphibian species, 16 bird species, seven mammals, and 1,600 flowering plants which are not found elsewhere in the world. The Government of India established many protected areas including 2 biosphere reserves, 13 National parks to restrict human access, several wildlife sanctuaries to protect specific endangered species and many Reserve Forests, which are all managed by the forest departments of their respective state to preserve some of the ecoregions still undeveloped. The Nilgiri Biosphere Reserve comprising 5,500 square kilometres (2,100 sq mi) of the evergreen forests of Nagarahole and deciduous forests of Bandipur in Karnataka, adjoining regions of Wayanad-Mukurthi in Kerala and Mudumalai National Park-Sathyamangalam in Tamil Nadu forms the largest contiguous protected area in the Western Ghats.[19]Silent Valley in Kerala is among the last tracts of virgin tropical evergreen forest in India.[20][21]

In August 2011, the Western Ghats Ecology Expert Panel (WGEEP) designated the entire Western Ghats as an Ecologically Sensitive Area (ESA) and assigned three levels of Ecological Sensitivity to its different regions.[22] The Western Ghats Ecology Expert Panel, headed by ecologist Madhav Gadgil, was a committee appointed by the Union Ministry of Environment and Forests to assess the biodiversity and environmental issues of the Western Ghats.[23]Gadgil Committee and its successor Kasturirangan Committee recommended suggestions to protect the Western Ghats. Gadgil report was criticized as being too environment-friendly and Kasturirangan report was labelled as being anti-environmental.[24][25][26]

These hill ranges serve as important wildlife corridors and forms an important part of Project Elephant and Project Tiger reserves. The largest population of tigers outside the Sundarbans is in the Western Ghats where there are seven populations with an estimated population size of 336 to 487 individuals occupying 21,435 km2 (8,276 sq mi) forest in three major landscape units spread across Karnataka, Tamil Nadu and Kerala.[34] The Western Ghats eco-region has the largest Indian elephant population in the wild with an estimated 11,000 individuals across eight distinct populations.[35][36] The endemic Nilgiri tahr which was on the brink of extinction has recovered and has an estimated 3,122 individuals in the wild.[37] The Critically Endangered endemic Malabar large-spotted civet is estimated to number fewer than 250 mature individuals, with no sub-population greater than 50 individuals.[38] About 3500 lion-tailed macaques live scattered over several areas in the Western Ghats.[39]

Seasonal rainfall patterns of the Western Ghats necessitate a period of dormancy for its land snails, resulting in their high abundance and diversity including at least 258 species of gastropods from 57 genera and 24 families.[61] A total of 77 species of freshwater molluscs (52 gastropods and 25 bivalves) have been recorded from the Western Ghats, but the actual number is likely higher.[47] This include 28 endemics. Among the threatened freshwater molluscs are the mussels Pseudomulleria dalyi, which is a Gondwanan relict, and the snail Cremnoconchus, which is restricted to the spray zone of waterfalls.[47] According to the IUCN, 4 species of freshwater molluscs are considered endangered and 3 are vulnerable. An additional 19 species are considered data deficient.[47]

Of the 7,402 species of flowering plants occurring in the Western Ghats, 5,588 species are native or indigenous and 376 are exotics naturalised and 1,438 species are cultivated or planted as ornamentals. Among the indigenous species, 2,253 species are endemic to India and of them, 1,273 species are exclusively confined to the Western Ghats. Apart from 593 confirmed subspecies and varieties; 66 species, 5 subspecies and 14 varieties of doubtful occurrence are also reported and therefore amounting 8,080 taxa of flowering plants.[62]